Thermal Engineering Design Project: A Linear Thermal Expansion Apparatus

Abstract

A thermal engineering design project requiring the design, construction, and operation of an apparatus that determines the liner thermal expansion of a slender aluminium rod is described in this paper. The author's design employed a radially constrained and axially free aluminium rod in an electrically heated, copper-tube oven. Thermal expansion was measured with a lever-arm rotating a mirror that reflected a laser beam. A class of junior (third year) mechanical engineering students, working in teams, produced designs using specifically designed air ovens, direct heating with an electric resistance wire wrap, and hot-water baths. Thermal expansion measurements employed dial gauges, dial callipers, micrometers, optical projections including laser beam reflection, and strain gauges. A plot of the accumulated data, comprised of 466 data points, produced a linear curve-fit whose slope gave the average coefficient of linear thermal expansion over the temperature range 20°C to 100°C. Most of the data clustered rather well around the published coefficient of liner thermal expansion line.